Adjustable counterweight for lift vehicles



A -21, 1956 E. s. MARNON EI'AL 2,759,563

ADJUSTABLE COUNIERWEIGHT FOR LIFT VEHICLES I Filed Sept. 13,1952 3 Sheets-Sheet l 8 l v 7- I Inveni'ors Edward S.Marnon,

' 'M/iJJiam'H Cook, ,Geqrge F Zier. I

Aug. 21, 1956 E, s. MARNON ET AL ADJUSTABLE COUNTERWEIGHT FOR LIFT VEHICLES Filed Sept. 13, 1952 3 Sheets-Sheet 2 Inven-I'ons' Edward .5. Mczrnon, Vfl'lliam Cook,

George F Zier. 7

Aug. 21, 1956 E. s. MARNON ET AL 2,759,563

ADJUSTABLE COUNTERWEIGHT FOR LIFT VEHICLES s Sheets-Sheet 3 Filed Sept. 15, 1952 United States Patent ADJUSTABLE COUNTERWEIGHT FOR LIFT VEHICLES Edward S. Marnon, Oregon City, George F. Zier, Milwaukie, and William H. Cook, Jennings Lodge, Greg; said Zier and said Cook assignors to said Mal-non Application September 13, 1952, Serial No. 309,504

2 Claims. (Cl. 187-9) This invention pertains to systems for moving weights between alternate positions, and relates particularly to a novel arrangement of supporting and actuating levers for shifting a counterweight between alternate positions with rapidity and with minimum power.

There are many industrial applications wherein the use of a movable counterweight is of recognized advantage. Among these is the counterbalancing 'of industrial cranes, steam shovels and lift trucks for purposes of maintaining a balanced condition during operation under varying conditions of load and position.

it is a principal object of this invention to provide a system for supporting and shifting a counterweight between alternate positions, in which system the counterweight is utilized effectively as a force in moving itself to said alternate positions.

Another important object of this invention is the provision of a system for supporting and shifting a counterweight between alternate positions, in which system external power is required for moving the counterweight only a portion of the distance between said alternate positions, thereby effecting the change of position of the counterweight with a minimum of external power.

A furher object of this invention is to provide a counterweight supporting and shifting system which is of simplified and sturdy construction, which operates rapidly and smoothly and requires a minimum of maintenance.

These and other objects and advantages of the present invention will appear from the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 is a side elevational view of a lift truck embodying the counterweight supporting and shifting system of this invention, the counterweight being shown in extended position;

Figure 2 is a side elevational view of the lift truck shown in Figure 1, the counterweight being retracted into the truck from the extended position shown in the preceding view;

Figure 3 is a fragmentary side elevaton of the rear portion of a lift truck showing details of the actuating mechanism for the counterweight assembly;

Figure 4 is a fragmentary side elevation of the counterweight assembly of the lift truck, the elements of the same being shown in extended position in dotted outline;

Figure 5 is a fragmentary sectional view taken along the line 55 in Figure 4; and

Figure 6 is a fragmentary side elevation as viewed from the right in Figure 5.

The counterweight shifting system of this invention is illustrated in the drawings and described hereinafter by its application to an industrial lift truck described and claimed in our copending application, Serial No. 309,503, filed September 13, 1952, and entitled Multi-Capacity Lift Truck.

Referring particularly to Figures 1 and 2 of the drawings, the lift truck comprises a vehicle frame 1 and body 2 mounted upon a pair of forward drive wheels 3 and a rear wheel unit 4 which is rotatable about a vertical axis by means of a steering assembly controlled by steering wheel 5 disposed in front of the operators seat 6. A pair of spaced unstanding masts 7 are secured pivotally adjacent their lower ends to the forward end of the vehicle frame and are connected to power means (not shown) by which they may be tilted forwardly and rear- Wardly in manner well known in the art. A pair of load-supporting forks 8 are supported slidably on the masts for movement longitudinally of the latter, said movement being effected by such means as the power driven chains 9 or other conventional mechanism.

Referring now to Figure 4 of the drawings, the rearward end of the frame 1 is stepped down and is adapted to receive thereupon a massive counterweight 11. The lower central portion of the counterweight is hollow in order to accommodate certain elements of the mechanism hereinafter described. The counterweight is suspended pivotally at its upper end upon shafts 12 which extend through brackets 13 secured to the counterweight, the shafts being supported in suitable bearings provided in the upper end of the transversely spaced support arms 14. Arms 14 are pivotally mounted at their lower ends on shafts 15 secured to the vehicle frame 1.

It is to be noted that when the counterweight is at rest upon the step portion of frame 1 the axis of shafts 12 is disposed in a plane normal to the frame forwardly of the axis of shafts 15. By this arrangement the Weight of counterweight 11 functions effectively to maintain itself inthe retracted position shown in full lines in Figure 4, thereby obviating the necessity of additional restraining force, as explained in greater detail hereinafter.

A shaft 16 is mounted for axial rotation transversely of the vehicle frame, forwardly of the stepped-down portion of the latter. Secured at one end adjacent the opposite ends of shaft 16 for rotation therewith is a lever arm 17. The free end of each lever arm is connected pivotally by link 18 to support arms 14 intermediate the ends of the latter, and by link 19 to opposite sides of the counterweight 11.

A single lever arm 21 is secured at one end to shaft 16, as by key 22, for rotation therewith. The free end of arm 21 is pivotally connected to the free end of a drive rod 23 which is secured at its opposite end to a piston 24 mounted slidably within the cylinder 25 of a conventional double-acting hydraulic ram. Cylinder 25 is pivotally secured at its end opposite rod 23 to the vehicle frame 1 by means of pin 26, as shown in Figure 3.

Flexible conduits 27 and 28 communicate at one end with the cylinder 25 at opposite sides of piston 24. The opposite end of each conduit is connected to a reversing valve 29 which, in turn, is connected to fluid lines 31 and 32 leading, respectively, to fluid reservoir 33 and to the output of fluid pump 34. Conduit 35 leads from the reservoir to the input of the fluid pump. Valve 29 is of the type which, when actuated to one position interconnects conduit 27 with line 31 and conduit 28 with line 32 and, when actuated to another position interconnects conduit 27 with line 32 and conduit 28 with line 31. In this manner fluid from pump 34 may be directed to either side of piston 24, the exhaust side of the cylinder being returned to reservoir 33.

Valve 29 also has an intermediate neutral position at which fluid lines 31 and 32 are interconnected to circulate the fluid from pump 34 to reservoir 33. In this neutral position conduits 27 and 28 are blocked from each other and from lines 31 and 32. Thus, fluid in cylinder 25 is prevented from flowing and the counterweight may thereby be locked in any position desired.

The valve 29 is actuated to its alternate positions by means of a pair of electrically operated solenoids 36 and 37 arranged in parallel electrical circuits and energized by the electrical supply source 38. Normally closed nucroswitches 39 and 40 are arranged in series in the electrical circuits of the. solenoids 36 and 37, respectively. These microswitches, hereinafter called limit switches, are mounted on frame 1 adjacent arm 21 for engagement therewith, as best shown in Figure 4; By this arrangement microswitch 40 is open when the counterweight is fully retracted and microswitch 39 is opened when the counterweight is full extended, thereby deenerg zing solenoids 36 and 37 and returning valve 29 to its, neutral position. The fluid purnp 34 is thereby relieved of unnecessary work when the counterweight is in, either of its extreme positions of retraction and extension.

Also arranged in series in the electrical circuits of solenpids 36 and 37 are the; normally open microswitches 41 and, 42, respectively, for controlling the operation of the solenoids, as explained in detail. hereinafter. These microswitches are mounted in vertically spaced relation in such manner as to receive one end: 43' of a switch arm 44; between them. The switch arm is mounted pivotally intermediate its ends on pin 45 carried by bracket 46 secured to the, vehicle frame. 1, the opposite end 47 of the, arm. extending; toward the rear of the vehicle. A tension spring 48; is connected at one end to the switch arm 44 forwardly of the pivot support 45. and at the opposite; end, toa bracket 49 secured to the vehicle frame above the arm 44. The spring thereby prevents the switch arm from. rotating of its own weight counter-clockwiseabout its pivot support 45.

Referring now to Figures and 6 of the drawings, the rear; steering wheel unit 4. preferably comprises a pair of wheels 51 mounted for rotation on an axle 52 by means of bearings 53. The axle is supported at itsends in the spaced sides 54' ofa rectangular frame and secured thereto by bolts 55'; A structural fender 56 overlies the wheels. and. is: pivotally secured at its forward end by pin 57: to a projection 58 on the forward end of the axle-supporting frame. Rearwardly extending brackets 61 and Marc provided on the rear-ward ends of the axlesupportingframe and fender, respectively.

A pair of coil springs 63 extendbetween the brackets 61; 62; the ends of the-springs encircling projecting studs 64 on thebrackets to prevent displacement ofsaid springs. The function of thecoilv springs is as follows, reference being made to Figure-6 of'the drawings: Since frame 1 restsnupon fender 56 and the latter is-pi'votally connected at its forward end' by-pin 57 to-the axle-supporting frame 54*, it is apparent that'the-weight of frame 1 impressed on pin=57 tends to rotate the sides 54 of the axle-supporting frame in a counterclockwise direction about axle 5-2. Bracket 61 thereby tends to move upwardly toward bracket- 62. Thus, the coil springs 63 function to resistthis counterclockwise rotationv and, in effect, provide a resilient'support for frame 1' on axle 52;

A, stepped shaft 65 is secured at itslower end to the fender 5,6. and extends vertically therefrom through an apert1 1r e 6.6 in thevehicle framev 1. Abearing 67 is interposed between the frame 1. and. the lowermost shoulder of,sha ft 65 to support the. frame thereon andfacilitaterelative rotation between said shaft andframe. A gear 68 is secured removably to the intermediate steppedportion of shaft, 65-" by means.of;bolt 69. Gear 6S'is connected through conventional mechanism (not shown) to, the steering wheel 5 by which the wheel unit 4 is rotated and .the vehicle is guided.

A rod 71' extends slidably-through-a bore 72 formed vertically through the axis of shaft 65and through fender 56. The lower end of rod 71 is connected to a flange 73 extending from a circular sleeve,74' which-freely excircles the axle 52 between the wheels 51; The upper end of rod 71 contacts the head 75 ofan adjustment screw 76 which is threaded into the rear end 47'of the switch arm 44. A lock nut 77 is employed to secure the screw 76 in any desired position of adjustment.

The operation of the mechanism described hereinbefore is as follows: With the lift truck in an unloaded condition and counterweight 11 is in retracted position on frame 1, adjustment screw 76 is set so that the forward end 43 of switch arm 44 is positioned in contact with microswitch 42. But since counterweight 11' is fully re tracted, limit switch 40 is opened by contact with arm 21 and therefore the circuit of solenoid 37 remains deenergized and valve 29 is in its neutral position, preventing the flow of fluid pressure to either side of piston 24 in the hydraulic cylinder 25.

When the operator engages the lifting forks 8 under a load 80 and starts to elevate the forks, as in Figure l, the weight of the load causes the frame 1 to tilt forwardly, i. e. the coil spring 63 supporting the rear end of the vehicle frame 1 on the axle frame extends because of the forward shift of the center of gravity. The extension of coil spring, 63 elevates the rear end of the vehicle frame 1 with respect to the forward end thereof. This elevation of the rearward end of frame 1 in turn causes elevation of the pivot support 45 of. switch arm 44. Since the rearward end 47 of the switch arm rests upon the upper end of rod 71, and since rod 71 is secured to the axle 52 of the rear wheel unit 4 which has not become elevated, switch arm 44 pivots clockwise about pin 45 and the forward end 43 of the switch arm is caused to rise toward microswitch 41.

It will be apparent that the lift truck is capable of lifting a certain maximum load with the counterweight retracted without becoming unbalanced to any serious degree. For purposes of illustration let it be assumed that this maximum load is one ton. Accordingly, microswitch 41 is so adjusted vertically above the foregoing initial position of the forward end 43' of switch arm 44 that a load of at least one ton must be applied to the lifting forks 8- before the forward end 43 of the switch arm will be-swung upwardly into contact with microswitch 41.

Assuming that load 80 isin excess: of the exemplified maximum, closure of microswitch 41 completes the electrical circuit of solenoid 36 which thereupon moves fluid valve 29 to the position at which fluid lines 32 and 28 are interconnected and fluid lines- 31 and 27 are also interconnected; Fluid pressure from pump 34 is thereby injected' into the right-hand end of cylinder 25' (Figure 3 to move piston 24 totlie left.

As piston 24 and rod 23 move to the left, shaft 16 is rotated in a clockwise direction (Figure 4) and the upper end of lever 17' begins tomovein the direction of arrows 31. Links 18exert a forceagainst counterweight support arms 14, causing the latter to pivot clockwise about shafts 15. The upper end of arms 14 swing inthe direction of arrows 8'2 inFigure 4, carrying'the suspended counterweight 11 rearwardly.

Fluid pressure against piston 24 is required only to pivot the support arms 14" clockwise until the axis of counterweight support shaft 12' passes rearwardly of the vertical plane of the axis of shafts 15; The weight of'the suspended counterweight 11 is then sufficientto swing the supporting assembly rearwardly to the position shown in dotted lines in Figure 4, at which the counterweight is It is to be pointed out here that the counterweight 11' is extendedrearwardlyby only the distance required. to oifset the load. 80. andthereby achieve optimum balance and stability of'the lift truck. As an illustration, let'it be assumed that the counterweight will extend fully. only when the load being lifted exceeds three tons. Thus,

when lifting a load of, say, two tons, counterweight 11 will'be extended'to some position intermediate the extreme limits of retraction and extension. At that intermediate position of extension the lift truck will be stabilized, and the rearward end of frame 1 will be lowered sufiiciently to move the forward end 43 of switch arm 44 downwardly out of contact with microswitch 41 to a position in between the microswitches 41, 42. Solenoids 36, 37 there by both being deenergized, valve 29 is returned to neutral position and the fluid in cylinder 25 is rendered immobile. Thus, since piston 24 is locked against further movement in either direction, the counterweight is retained in the proper position of extension.

With the counterweight extended rearwardly as described hereinabove the center of gravity of the vehicle is effectively shifted rearwardly to compensate for the additional weight of load 80 supported forwardly of the front wheels 3. It is to be observed in Figure 4 that when the copnterweight is fully extended it is not only extended rearwardly of the frame, but it is also lowered to a level substantially below its normal rest position on the frame. This lower position effectively lowers the center of gravity of the vehicle and thereby stabilizes the latter to an even greater degree.

It will be understood that when the counterweight is fully extended, as shown in dotted outline in Figure 4, arm 21 contacts and opens limit switch 39. Thus, the circuit of solenoid 36 is opened and valve 29 is returned to neutral position. In this manner the fluid pump 34 is relieved of unnecessary work in holding the counterweight in its fully extended position.

The operator now manipulates the proper controls which first tilts the masts 7 rearwardly and then elevates the load to a position on the masts at which the center of gravity of the vehicle is shifted rearwardly a distance sufiicient to cause the rearward end of the vehicle frame 1 to be lowered against the compression of spring 63 until the pivot support 45 of switch arm 44 is lowered to a point at which the forward end 43 of said arm is moved downwardly from its intermediate position into contact with microswitch 42. The closing of microswitch 42 energizes solenoid 37 which moves fluid valve 29 to the station at which fluid lines 32, 2'7 and 31, 28 are in respective communication. Thus, fluid pressure from pump 34 is injected into the left-hand end of cylinder 25 to drive the piston 24 rearwardly (to the right in Figure 3). Shaft 16 thereupon rotates counterclockwise, moving the assembly of lever arms 17, links 18, 19, support arms 14 and counterweight 11 to the left in Figure 4 to the position of rest shown in full lines. The vehicle is now ready to transport the load.

In returning the counterweight to retracted position it is to be noted that as shafts 12 pass forwardly beyond the vertical plane of shafts 15 no further fluid pressure is required because the weight of the counterweight is suflicient to complete its own retraction from that stage to its final position of rest upon frame 1. In this position limit switch 44 is opened, solenoid 37 is deenergized and valve 29 is returned to its neutral position.

From the foregoing it is seen that the counterweight functions by extending rearwardly of the vehicle automatically and to the proper extent to counterbalance the vehicle during the preliminary stages of lifting and tilting the particular load. Then, when the load is elevated rearwardly on the masts to a point of stability the counterweight is retracted automatically, thereby reducing the length of the vehicle to its minimum dimension shown in Figure 2 for most efficient maneuverability during transportation of the load.

Further, it is apparent that the counterweight extends and retracts automatically as the vehicle travels over uneven paths and inclined surfaces which are of sufficient magnitude to cause movement of the switch arm 44 alternately into contact with microswitches 41 and 42. Thus, proper balance of the vehicle is maintained automatically under all of the usual adverse conditions of travel, and the counterweight is actuated with such speed that balance 6 is maintainedeven when the center of gravity of the truck is shifted rapidly.

The arrangement of the shafts 12 and 15 with respect to the supporting arms 14 for the counterweight 11 is of particular advantage in the present invention. In the initial stage of extension, the counterweight is required to be lifted vertically as it moves rearwardly until shafts 12 pass the vertically plane of shafts 15. Fluid power is required to effect this movement only, thereby reducing the power requirements to a minimum and effecting extension of the counterweight with maximum speed. Moreover, since the weight of the counterweight resists its own elevation during this initial stage, the counterweight functions to prevent its own accidental extension while in its retracted position of rest upon the vehicle frame.

It will be apparent to those skilled in the art that the counterweight system described hereinbefore may be applied to advantage in other types of apparatus. The basic requirements for adaptation of the provision of a frame for supporting the counterweight assembly and some form of power for actuating the lever 17. The power source may be controlled by the electrical system describing herein, or it may be controlled by any other convenient or desired system. Further, the power control system need not be actuated by the tilting of the supporting frame, for there are various other modes of operation, including manual control, which may be utilized.

It will also be apparent to those skilled in the art that various changes in the structural details described hereinbefore may be made without departing from the scope and spirit of the present invention. Accordingly, it is to be understood that the foregoing description is merely illustrative and is not to be construed in a limiting sense.

Having now described our invention and the manner in which the same may be used, what we claim as new and desire to secure by Letters Patent is:

l. A system for shifting a counterweight between retracted and extended positions, comprising, in combination with a counterweight, a supporting frame, a pair of spaced support arm means each mounted pivotally at its lower end on the frame, pivot means suspending the counterweight between the upper ends of the support arm means, the axis of the counterweight pivot means being displaced alternately on opposite sides of the plane of the pivotal mounting of the support arm means, which plane extends normal to the plane of the frame, when the counterweight is in retracted and extended positions, lever means mounted pivotally on the frame, link means pivotally connecting the lever means with the support arm means, link means pivotally connecting the lever means with the counterweight for stabilizing the latter, and reversible power means connected to the lever means for rotating the latter whereby to extend and retract the counterweight.

2. A system for shifting a counterweight between retracted and extended positions, comprising, in combination with a counterweight, a supporting frame, support arm means mounted pivotally at its lower end on the frame pivot means suspending the counterweight from the upper end of the support arm means, the axis of the counterweight. pivot means being displaced alternately on opposite sides of the plane of the pivotal mounting of the support arm means, which plane extends normal to the plane of the frame, when the counterweight is in retracted and extended positions, lever means mounted pivotally on the frame, link means pivotally connecting the lever means with the support arm means, link means pivotally connecting the lever means with the counterweight for stabilizing the latter, and reversible power means connected to the lever means for rotating the latter whereby to extend and retract the counterweight.

(References on following page) References Cited in the file of this 'patent' UNITED STATES PATENTS Welin June 8, 1920 Holmes June 23, 1925 Molinelli Sept. 24, 1935 Irish Jan. 11, 1938 Cal-dwell Nov. 4, 1941 Schroeder Aug. 24, 1943 8 Spiegel Jan. 30, 1945 West Oct. 1, 1946 Schreck Apr. 18, 1950 Eakin Nev. 13, 1951 Vance July 15, 1952 FOREIGN PATENTS Great Britain June 14, 1862 

